Depending how aggressive or conservative a BRM guideline you want to use, your solid win rate indicates you can try moving up if you have enough buyins. 20 would be on the aggressive end; for most people, I tend to suggest 30 so as to have a decent buffer against being forced to drop back if you hit a small down streak right away.

If you don't have enough in your roll, I'd still take $20 or maybe $30 to test out NL10 and see how it feels to you (focus more on that than whether you win or lose). If you don't feel too uncomfortable, you just have to grind some more NL5 to build up your roll enough to move up.